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Three-dimensional elemental mapping of hollow Fe2O3@SiO2 mesoporous spheres using scanning confocal electron microscopy
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Image of FIG. 1.
FIG. 1.

(a) Schematic of the three-window technique. The core-loss signal is obtained from the post-edge by subtracting a background which is estimated using two pre-edge images and fitting a background model of the form AE−r. (b) Schematic of ray paths for SCEM, showing that beams (····) scattered away from the confocal point are rejected by the collector aperture. (c) Schematic illustrating a core ca.100 nm in diameter attached to the inside of the wall of a hollow sphere ca. 600 nm in diameter. The centre of the core is assigned as the origin of the scanning coordinates, with the z axis the optical axis or sample depth direction.

Image of FIG. 2.
FIG. 2.

(a) and (b) Si core-loss signals from x-y and x-z scans, respectively, using the “three-window” technique; (c) and (d) HAADF x-y and x-z scans, respectively, of the same region. The dotted-square indicates the area (16 × 16 pixels) from where the noise level of 11 arbitrary intensity units was calculated.

Image of FIG. 3.
FIG. 3.

(a) and (b) Single pixel width line profiles extracted across the inner core at the positions labelled with arrows in Figs. 2(a) and 2(b), respectively. The value of the error bar is ±11, which is the standard deviation calculated from the region labelled with a dotted square in Fig. 2(a). The two sides of the core are indicated by red arrows.

Image of FIG. 4.
FIG. 4.

Schematic procedures for the formation of hollow inner core structures. The blue hatched regions represent a mesoporous silica coating; the black sphere and red dots represent the carbon sphere and adsorbed Fe source, respectively. (a) A colloidal carbon sphere adsorbed with an iron precursor and a coating of tetraethoxysilane and n-octadecyltrimethoxysilane prior to calcination. (b) During calcination, a thin part of SiO2 coating layer (blue hatched) becomes detached from the main outer SiO2 sphere. (c) A central self-supporting Fe and SiO2 spherical framework is formed once the carbon template is completely removed.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Three-dimensional elemental mapping of hollow Fe2O3@SiO2 mesoporous spheres using scanning confocal electron microscopy